Abstract
The marine diatom Phaeodactylum tricornutum is an important basal resource in the marine food chain and is used as a standard test organism in toxicological studies. In this study, in vivo experiments were performed to analyze the effects of 1-octyl-3-methylimidazolium bromide ((C8mim)Br) on the growth, photosynthetic activity, and antioxidant enzymes of P. tricornutum using 96 h growth tests in a batch-culture system. The results showed that (C8mim)Br significantly inhibited the growth of P. tricornutum, with a 96 h EC50 of 8.89 mg l �1 , and likely restricts PSII electron transfer and light use efficiency of the diatom. With increasing (C8mim)Br concentrations, the soluble protein content in the diatom increased by 35.9, 58.5, 123.3, 197.7, and 207.0% in 5, 10, 20, 40, and 80 l �1 (C8mim)Br treatments relative to the controls, respectively. Concentrations of (C8mim)Br ≤10 mg l �1 caused a slight increase of superoxide dismutase (SOD) activity (from 16.37 to 23.04 U g �1 protein) in the diatom, but inhibited its activity at concentrations above 10 mg l �1 . These observations indicate that moderate (C8mim)Br stress (about 10 mg l �1 ) likely stimulates the synthesis of proteins and free radical quenching. The general increase in malondialdehyde (MDA) content suggests that the physiological effects of (C8mim)Br were caused by free radical genera- tion. Thus, potential risks exist if (C8mim)Br is accidentally released into the aquatic environment.
Highlights
Ionic liquids (ILs), composed of a bulky organic cation and organic or inorganic anions, are environmentally friendly replacements for industrial volatile organic compounds because of their relatively low melting point (Pham et al 2010)
Growth inhibition increased with increasing exposure time from 0 to 96 h (e.g. an increase in growth inhibition may be related to the cell wall structures of different microalgal species, since the cell wall plays an important role in the transport of materials in and out of the cell (Kulacki & Lamberti 2008, Samorì et al 2011)
After 24 h exposure, Fv/Fm and Fv/F0 showed no significant differences at [C8mim]Br concentrations of ≤20 mg l−1 (p > 0.05), but there were slight decreases (73.8 and 65.6% of that in controls, respecfrom 0 to 76.0% in 80 mg l−1 [C8mim]Br treatments) and increasing [C8mim]Br concentration from 5 to 80 mg l−1
Summary
Ionic liquids (ILs), composed of a bulky organic cation and organic or inorganic anions, are environmentally friendly replacements for industrial volatile organic compounds because of their relatively low melting point (Pham et al 2010). The main advantage of ILs is the significantly lower risk of industrial exposure and solvent loss to the environment. ILs are very stable and soluble in water (Bruzzone et al 2011), which may potentially lead to water pollution and related risks once the ILs enter an aquatic environment Recent studies have documented that ILs have toxic effects on aquatic organisms such as algae (Latała et al 2009, 2010, Das & Roy 2014), cladocerans (Couling et al 2006, Luo et al 2008, Pretti et al 2009, Ventura et al 2010), mussels (Costello et al 2009), and fish (Pretti et al 2009, Cvjetko Bubalo et al 2014). The effects of ILs on aquatic organisms consist of ‘alkyl side chain’ effects (an increase in antimicrobial activity with the elongation of the alkyl chain) and the ‘cut-off’ effect (beyond a given chain length, the effects cannot increase any further) (Ventura et al 2012).
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